Position sensor assemblies arranged to determine/follow the position of a valve in the cylinder of a combustion engine are known since long. Early variants of position sensor assemblies were, however, not sufficiently fast and exact to be usable in connection with objects moving at very high speed, such as valves in a combustion engine in a car. In the car industry, there are additional requirements that the systems to be used should be robust and have great reliability at minimal cost. In recent years, systems have appeared that comprise a stationary coil/inductor that interacts with a movable body manufactured from an electrically conductive material, said movable body being connected to the valve and moving together therewith.
See, for instance, U.S. Pat. No. 7,032,549, which discloses a position sensor assembly comprising an oscillator, a first body, a coil, a control unit, and a sensor circuit, said first body being reciprocally displaceable in the axial direction in relation to and externally of said coil. The sensor circuit comprises in turn a comparator connected to a first branch comprising said coil, an oscillator, and a measuring resistance coupled in series with each other. When the coil is energized, it is arranged to generate an oscillating magnetic field, which in turn induces eddy currents in the displaceable body, which causes the coil to be short-circuited. The degree of short circuit of the coil changes proportionally to the change of the mutual overlap between the coil and the body. Then the comparator determines the position of the valve based on the phase shift between the supply voltage of the oscillator and the voltage across the measuring resistance, the phase shift increasing with increasing overlap between the coil and the body.
However, said position sensor assembly is impaired by the disadvantage that the same comprises an oscillator, or a similar signal generator that provides an alternating voltage signal, which, relatively speaking, is energy demanding since the oscillator continuously is in operation. Furthermore, said method comprises partly analog signals, which entails that the mutual position only can be determined with, relatively speaking, low time and location resolution.